The invention relates to a method and an apparatus for regulating the fuel-air mixture provided to an internal combustion engine. The regulation includes the supply of supplementary air to be added to a fuel-air mixture generated in a mixture generator in dependence on the operational state of the internal combustion engine.
In a known method of this type, the oxygen content of the exhaust gases is monitored and additional air is metered out by a by-pass valve in dependence on the exhaust gas oxygen content. In that system, an electronic controller determines the throttle position as well as the engine rpm to define a basic setting of the by-pass valve while the oxygen content in the exhaust gases superimposes a further opening motion of the valve. This type of known regulation requires a fairly substantial and expensive controller. Furthermore, the quantity of actually aspirated fuel-air mixture can be determined only by the throttle valve position together with the rpm signal or the vacuum in the induction tube. Thus, two measured quantities are required in order to find the parameter whose exact measurement is most important and that parameter is then processed to provide a setting signal for the by-pass throttle valve.